Various Types of Imaging Modalities - Essay Example

?Choices for Imaging Modalities The process by which humans and the environment are protected from the harmful effects of ionizing radiation and at the same time taking advantage of its important applications is known as radiation protection (Stabin, 2007, p. 1). To ensure that there is no alarming damage to people undergoing and facilitating diagnostic imaging, precautions are undertaken such as shielding of equipment by the use of leaded glass shields, as well as the use of dosimeters and using digital equipment to capture images with less exposure to radiation (Smith, 2007, p. 13). Dosages of radiation can have a multitude of effects on patients, whether pregnant or not. In order to avoid the over-exposure of patients to lethal dosages, several regulations are implemented not just for their safety, but for the safety of radiologists as well (Consultant Physicist Radiation Protection, p. 6). For most patients, there is the Ionising Radiation (Medical Exposures) Regulations 2000 practitioners, or IRMER practitioners, which can either be the IRMER operator (does the exposing of patients under medical x-ray), IRMER practitioners (justifies the use of medical x-rays) and the IRMER referrer (Armoogum, p.10). By adhering to IRMER, the hazardous effects of radiation coming from diagnostic devices would be minimized since 1) all IRMER operators, practitioners and referrers must all have the same understanding that there are limits as to how long the exposure of a patient to medical x-rays or other diagnostics should be; 2) the IRMER practitioner and referrer must be registered health professionals, since they would have adequate knowledge in the type of diagnostic Under the Ionising Radiations Regulations 1999 or IRR99, employers whose purpose is offering diagnostic imaging services should take all of the necessary steps in restricting the use of ionising radiation among employees not capable of handling the equipment, as well as limiting their use among capable employees (Armoogum, p.8). There are various types of imaging modalities available for all patients, depending on their needs. Most of these may have a certain degree of radiation, depending on the source of energy or radioactive material (Lowe, p. 646). For pregnant women, it is highly recommended that the diagnostic service for them should not cause any teratogenic or birth effects on the foetus. Some examples of these are those that do not use electromagnetic radiation such as ultrasound and magnetic resonance imaging (MRI) without contrast. Ultrasound utilises high frequency sound waves which are generally longitudinal and moves along in a parallel fashion, and is dependent on the physical density of the object being scanned by the acoustic waves being sent, since there are different densities of tissues in the body (Hendee & Ritenour, 2002, p.3, & Serway & Jewett, 2008, p. 451, 492). In order for ultrasound waves to create images, waves are first propagated by sending oscillating waves through a medium (abdominal cavity), and depending on the density of the medium could get compressed, creating a low-pressure region behind it called rarefaction, and reflect and scatter back as echo being detected by the transducer. Dense tissue would absorb waves and create heat (e.g. bones), while less dense structures would not (e.g. amniotic fluid), assuming that the intensity of the wave being sent is the same all throughout (Nicolaides, Rizzo & Hecher, 2000, p. 26). If the distance between two successive compressions (or rarefactions) is short, the wave is said to be high-energy short wavelength and has a higher degree of penetration (Serway & Jewett, 2008, p. 476). Physical effects of ultrasound are generally categorized as thermal (tissue gets heated due to absorption), cavitation (formation of gas bubbles at high negative pressure), and other mechanical effects to tissues (Nicolaides, Rizzo & Hecher, 2000, p. 26). Visualisation of blood flow can be shown via B-mode or real-time ultrasound, where there would be colour representations of blood flow which label it either towards or away from the probe (Stocksley, 2001, p. 21). On the other hand, chemical bonding of molecules such as hydrogen affect MRI output, because the strength of magnetic fields (Gauss in lower strength magnetic fields, Tesla for higher magnetic fields) in the different parts of the body provide the image during an MRI scan. Radiofrequency coils (RF coils) send pulses that would react with the hydrogen in the tissues to be scanned, and the signals that would be sent back (echo) would be received again by the RF coils and interpreted as a measureable signal (Buxton, 2002, p. 78). This echo signal would be decaying by a fast half-life (T2), but if another RF pulse is sent at an interval after a delay (TE/2), the corresponding echo would be a lot stronger compared to the previous echo. This can be sustained by continuously sending RF pulses at specific intervals (TR) to lengthen the formation of echoes, however the strength of the signals would still be affected by the rapid decay of the echo (ibid., p.81). Hydrogen bonded to water will behave differently when bonded with carbon in fats, thus the different resonant frequencies being observed during scans (Roth & Seeram, 2002, p. 54). At the resonant frequency of a bound atom it can absorb electromagnetic energy from a RF pulse during its release and return a portion of the signal back as an echo, which is dependent on its location and bonding as well as fluctuating dipole fields due to nearby nuclei or unpaired electrons (Buxton, 2002, p.179). Additional clarity can be achieved by using contrast dyes which affect the magnetic field and the relaxation times of the tissues and would be dependent on whether T1 (initial pulse) or T2 (half-life decay of T1) would be focused on. Shorter T1 would show brighter tissues, and shorter T2 would appear dark (Roth & Seeram, 2002, p. 56). However, the use of intravenous contrasting dyes such as gadolinium are not recommended because as previously mentioned, anything that enters the mother’s bloodstream could affect the foetus in some way (Lowe, p.374). Another example of diagnostic services that are safe to use for pregnant women is computed tomography (CT), although radiation shielding and the radiopharmaceutical doses used for providing images with contrast such as barium-based ones would become the deciding factor on whether a procedure would be safe for the foetus or not (Lowe, p. 647). This type of scan utilises X-ray beams shooting at different angles to form a composite image (Bushberg et al., 2002, p. 363). However, despite being regarded as advanced over traditional X-rays, CT delivers a higher dose of ionising radiation as compared to traditional radiography. Also, the tissues surrounding the area being scanned tend to scatter excess radiation, which could affect the foetus should the scanning be done around the abdomen (Parry, Glaze & Archer, 1999, p. 1297). Lastly, imaging that uses mostly nuclear medicine for visualisation of internal organs such as positron-emission tomography (PET), abdominal X-rays (AXR) and endoscopic retrograde cholangiopancretography (ERCP) are avoided as much as possible since there are radioactive elements involved in the process of getting the images of the patient, such as injection of detection dyes (Hendee & Ritenour, 2002, p. 3). These dyes could enter the bloodstream and pass into the foetus’ body via the placenta. Since a foetus is rather small and has low mass density, it could easily get bombarded by powerful particles through the emission of such diagnostic devices, which can either kill it or cause deformities in its development (Klossner, 2006, p. 108). Several effects of excess radiation exposure among foetuses have been determined. These can be either deterministic or stochastic (Bushberg et al., 2002, p. 795). The deterministic effect of excess radiation exposure in cells is that the cells are killed instantly, thus the prevention of the proliferation of the cell line, and eventually causing massive cell death in the area that absorbed radiation (Bushberg et al., 2002,, p. 795). These would cause an overall negative effect in the normal function of the organ, or in a pregnant woman’s case, the growing foetus (Koukouliou et al., 2008, p. 6). CT scan, although somewhat much more advanced than conventional X-ray, still uses ionising radiation, which can affect the foetus, especially during the early trimesters (CDC, 2011, p. 1). Increased number of exposures as well as high doses of radiation delivered in a short amount of time can eventually cause cells to stop proliferating (Koukouliou et al, 2008, p. 7). This can be very dangerous to a growing foetus since there are always actively-dividing cells that can get destroyed, and may cause a decrease of cessation of functions in the body parts affected (Bushberg et al, 2002, p. 795). Excess exposure to radiation by the foetus could cause stunted growth, deformities, abnormal brain function or developing cancer such as leukaemia in later life, and although a foetus in the third trimester has more resistance to radiation than compared to early trimester foetuses, there are still chances of cancer development which can be avoided by non-exposure to ionising radiation (CDC, 2011, p.1). On the other hand, stochastic effects of radiation on cells are famously exemplified by the formation of cancer cells (Bushberg et al, 2002, p. 795). The normal cell division of cells become disrupted, and cells that normally stop dividing after several mitotic divisions become mutated in such a way that there is a continuous division of cells, which keep on stacking on one another until a mass of cells are formed (Koukouliou et al, 2008, p. 7). More often than not, stochastic effects are caused by low doses of exposure to radiation, enough to mutate the cells but not enough to kill them. In order to prevent a radiation overdose in any patient, the science of radiation dosimetry is employed by people performing diagnostic imaging. This is particularly important especially for pregnant women, whose growing foetus could easily absorb high-energy rays due to less tissue density. Pregnant women can develop gallstones when the stones are not passed out of the bile ducts, or if there is a problem with the motility of the gallstones themselves (Hauser, 2004, p. 428). This causes pain in the epigastric region and radiates to the back, and last for several hours. When the stones cause obstruction of the bile duct, it is called cholecystitis (Powrie et al., 2010, p. 240). The formation of gallstones is determined by several factors such as geography and race, as well as age and nutrition (Hauser, 2004, p. 428). Repeated infection of the gallbladder ducts can cause chronic cholecystitis, a disease that manifests itself repeatedly, and causes the gallbladder to become impaired in functioning (Rubin & Reisner, 2002, p. 339). Symptoms can include fever, persistent pain in the abdomen, leukocytosis and chills. Hormonal changes during pregnancy could also actually cause disruption in the normal functions of the gallbladder, which includes decreased rate of bile fluid released, sluggish motility of the gallbladder, precipitation of cholesterol or calcium salt of bilirubinate, and increased saturation of cholesterol-saturated bile in the gallbladder. Such effects on the gallbladder will result to the formation of stones, which are rather difficult to pass out, causing pain to the patient (Salvi, 2003, p. 457). Management of a woman with gallstones in her third trimester of pregnancy could need extra precautions. Once detected, she should immediately seek medical help (Powrie et al., 2010, p. 240). Also, if possible, removal of stones should be considered, since at present, the removal by laparoscopic methods can offer a safer alternative, which has lesser foetal mortality than using conventional methods of management (Salvi, 2003, p. 459). Lastly, there should be monitoring of patient through the use of ultrasonography in detecting any additional abnormalities as well as for checking the foetus’s status while the mother is undergoing treatment. Due to some symptoms of cholecystitis being rather similar with signs of pregnancy such as nausea and vomiting, the disease has possibilities of not being detected early, which leads to the continuous formation of stones till the gall bladder becomes inflamed (Salvi, 2003, p. 457). Stones can also be removed either by traditional surgical methods in the early trimesters of pregnancy, or through laparoscopic cholecystectomy, which is not as invasive as surgery and safer in all trimesters of pregnancy (Hauser, 2004, p. 429). Early detection of gallstones must also be detected by diagnostic imaging that is safe for a growing foetus. In any kind of imaging, whatever method is used would cause certain interactions with the tissues or organs being examined (Bushberg et al., 2002 p. 3). This is important to know since the longer the exposure of tissues, although images that can be formed may be clearer, the cells that get exposed might have gotten a certain amount of damage. Ultrasound is a good choice for a pregnant woman who wants to have her gallbladder examined for stones. The waves are highly dependent on the density and acoustic properties of the surrounding tissues, which makes visualisation and contrast in ultrasound easier to interpret (Bushberg et al., 2002, p.14). For example, any body part with low density like the liver or intestines would register much fainter signals as compared to dense body parts like bones since bones would absorb the waves (echogenic), as opposed to internal organs which would reflect them (ibid., p. 12). Also, since medical ultrasound uses sound waves concentrated into a small area only, and relies on how much waves are reflected back, there is less chances of harming the growing foetus, as opposed to using X-rays, which shoot ionising high-energy beams and need attenuators to reduce exposure to it (Hendee & Ritenour, 2002, p.112, 306). Although relatively more advanced than X-rays, CT is still not recommended since it also utilises radiation, and does not give the exact high resolution images needed for visualisation of stones (Bushberg et al., 2002, p. 363). MRI can also be used however, it takes a longer time to produce clear images, which takes tens of minutes, and the patient must be rather still within this time frame (ibid., p. 10). Other diagnostic tests which utilise nuclear medicine such as PET and ERCP, if ever available, could still pose harm to the foetus because aside from using radioactive isotopes for visualisation, these also use high-energy beams for detection, which could again cause irreparable damage to regions of active cell division in a foetus. Therefore, the safest choice for a pregnant woman who would want to have her gallbladder inspected would be to have an ultrasound. It is a quick method of detection of stones, uses less time in exposure, and is relatively safe for her growing child since it only uses sound waves as means of visualisation, which do not release ionising radiation that can cause abnormalities and possible development of cancer. Bibliography Journal Presentation. 2004. Dundee, (2004). Ionising radiations regulations 1999 an overview. Armoogun, K. ed. Dundee, Ninewells Hospital Bushberg, J.T., Seibert, J.A., Leidholt Jr., E.M. & Boone, J.M. (2002). The essential physics of medical imaging. Philadelphia, Lippincott Williams & Wilkins Buxton, R.B. (2002). Introduction to functional magnetic resonance imaging: principles and techniques. Cambridge, Cambridge University Press Centers for Disease Control and Prevention (CDC). (2011). Radiation and Pregnancy: A Fact Sheet for the Public. Available from [Accessed March 2, 2012]. Hauser, S. (2004). Mayo clinic gastroenterology and hepatology board review. Oxford, Oxford University Press Hendee, W.R & Ritenour, E.R. (2002). Medical imaging physics. New York, Wiley-Liss Inc. Klossner, N.J. (2006). Introductory maternity nursing, volume 1. Philadelphia, Lippincott Williams & Wilkins Koukouliou, V. Ujevic, M. & Premstaller, O. (2008). Threats to food and water chain infrastructure. Dordrecht, Springer Nicolaides, K.H., Rizzo, G. & Hecher, K. (2000). Placental and fetal doppler. Oxon, Parthenon Publishing Group. Parry, R.A., Glaze, S.A., & Archer, B.R. (1999). The AAPM/RSNA physics tutorial for residents: typical patient radiation doses in diagnostic radiology. RadioGraphics, 19 September, pp. 1289-1302. Powrie, R.O., Greene, M. F. & Camann, W. ed. (2010). De Swiet’s medical disorders in obstetric practice. West Sussex, John Wiley & Sons Roth, C.K., & Seeram, E. (2002). Rad tech's guide to MRI: imaging procedures, patient care, and safety. Massachusetts, Blackwell Science Inc. Rubin, E. & Reisner, H.M. (2002). Essentials of Rubin’s pathology. Philadelphia, Lippincott Williams & Wilkins Salvi, V. (2003). Medical and surgical diagnostic disorders in pregnancy. New Delhi, Jaypee Brothers Medical Publishers Ltd. Serway, R.A. & Jewett, J.W. (2008). Physics for scientists and engineers, Volume 1. Belmont, CA, Thomson Higher Education Smith, A.D. (2007). Smith’s textbook of endourology. BC Decker Inc. Stabin, M.G. (2007). Radiation protection and dosimetry: an introduction to health physics. New York, Springer Science+Business Media LLC Stocksley, M. (2001). Abdominal ultrasound. Cambridge, Cambridge University Press. Appendices Figure 1. CT Scan of a gallbladder cancer patient, with visible stone Figure 2. MRI of gallbladder with stones in different areas Images courtesy of http://www.hpblondon.com/gallstones/ Appendices Figure 3. Ultrasound image of a gallbladder, red arrow points to a stone Figure 4. ERCP image of internal organs surrounding the pancreas Images courtesy of genesis-ultrasound.com and uppergisurgery.com.au/surgery/gastroscopy/ercp/ Appendices Figure 5. A sound wave Figure 6. Compression and rarefaction in a longitudinal wave Images courtesy of http://www.tutorvista.com/content/physics/physics-i/wave-motion-sound/longitudinal-and-transverse-waves.php and http://www.divediscover.whoi.edu/expedition12/hottopics/sound.html Appendices Figure 7. Concept of how MRI works Image courtesy of http://www.jwestdesign.com/concept/concept-3.html Read More